Duct system

ABSTRACT

An aluminum extrusion molding with multiple flanges for gripping and supporting both duct board paneling and longitudinal support members. Duct structures are made of the above molding in combination with duct board paneling wherein a single piece of molding is formed into a duct board frame defining the periphery of the duct. The molding gripping flanges have extended beads for gripping the duct board which beads also enhance the seal between molding and duct board.

United States Pate t Sherman et al.

[54] DUCT SYSTEM [72] Inventors: James Webster Sherman; James WilliamHelmick, both of Toledo, Ohio [73] Assignee: Johns-Manville Corporation,New

York, NY.

[22] Filed: June 29,1970

[21] Appl. No.: 50,595

[52] US. Cl ..138/109, 138/155, 138/DIG. 4, 220/80, 285/424 [51] Int.Cl. ..F16Z 9/22 [58] Field of Search..52/496, 730; 98/40 C; 138/103,138/106,109,149,l55,156,177,178, DIG. 2, DIG. 4, DIG. 8; 217/63; 220/80;285/424 [5 6] References Cited UNITED STATES PATENTS Deitsch ..285/424 XAug. 29, 1972 2,632,534 3/1953 Grey ..52/496 X 3,001,805 9/1961 Jones etal. ..285/424 X 3,078,880 2/1963 Stephens ..l38/DIG. 2 UX 3,092,5296/1963 Pearson ..l38/D1G. 2 UX Primary Examiner-Edward J. EarlsAttorneylohn A. McKinney and Robert M. Krone [5 7] ABSTRACT An aluminumextrusion molding with multiple flanges for gripping and supporting bothduct board paneling and longitudinal support members. Duct structuresare made of the above molding in combination with duct board panelingwherein a single piece of molding is formed into a duct board framedefining the periphery of the duct. The molding gripping flanges haveextended beads for gripping the duct board which beads also enhance theseal between molding and duct board.

10 Claims, 7 Drawing Figures PATENTED I973 3,687,168

INVENTORS JAMES W. SHERMAN JAMES W. HELM I CK ZJM'IIWL AT TORNFYS DUCTSYSTEM BACKGROUND OF THE INVENTION Duct work for ventilating andhumidity systems and the like traditionally was fabricated out of sheetmetal and covered with insulating materials. More recent developmentshave led to ducts constructed of insulating materials in the form ofboards or panels having sufficient rigidity to eliminate the requirementof a metal duct for certain uses. This type duct was constructed bystapling and taping the boards into, typically, a rectangular ductsection with each side of the duct consisting of a board. The requirednumber of duct sections were then butted end to end and the joints tapedto form a continuous duct of the desired length.

The taping served two functions: (1) it held the boards in a structuralshape which shape had sufficient stifiness to make the duct selfsupporting, and (2) sealed the duct making it an air tight structurethereby increasing its efficiency for the purpose of directing air orlike type gaseous flow.

Ducting so constructed was usually suspended from the ceiling of thestructure in which it was installed by means of wire or strap supportsin the form of slings passing underneath the duct periodically along thelength of the duct.

The problem with this type construction was the structural weakness ofthe duct and the tape joints, plus the lack of rigidity of the suspendedsystem which took on the nature of a suspended pendulum. The weakness ofthe taped joint, from the structural standpoint, prevented long spans ofducting between support points, and this problem was further aggravatedby the weakness of the insulating board material, which would sagbetween supports on long spans. Further, the weakness of the insulatingboard material put significant limitations on the duct system withrespect to the pressure differential between the inside and the outsideof the duct, since the board was subject to bowing.

Where the weakness problem was sought to be overcome by the addition ofsteel support members to join and support the boards, it was found thata leakage problem thereby arose between the supports and the board whichcould only be solved by duplication of effort. The joints had to betaped to seal them where steel was used to support the insulating board.

The present invention overcomes these problems with a duct board moldingand longitudinal support in combination with the molding forming a rigidstructural frame for the duct board in all directions. The framesupports both structurally and against system pressure differentialsallowing the suspension support points to be spread out, and provides arigid structure which can in turn be suspended rigidly in place.

in addition, the molding has a unique sealing characteristic when usedin combination with insulating duct board having resiliency when thefaces of the board are pressed together. Thus, the joints of molding tothe board do not have to be taped to obtain the desired seal.Elimination of the taping requirement overcomes the problem of having totape joints in place, which is especially troublesome when the duct isinstalled nearly flush to ceiling or walls.

SUMMARY The present invention relates to moldings and duct systems andmore particularly to moldings for use with duct board and duct systemsconstructed of duct board with molding for joints as well aslongitudinal supports.

The molding consists of an aluminum extrusion with flanges stacked oneabove the other and interconnected by a rectangular web attachedsymmetrically to and at right angles with the faces of the flanges. Theend flanges are attached to the edge of the web and extend over thelength of the web. One end flange is shorter in width than the other endflange and this other end flange has beads extending from the face ofthe end flange along the extremities of the end flange opposing liketype beads on the extremities of the face of the intermediate flange.These beads are continuous over the length of the flanges and exist onthe face extremities of the flanges on both sides of the web. The endflange, which is shorter in width, has a radius on the corners facingthe intermediate flange and extending over the length of the flange.

The molding in conjunction with paneling, such as duct board, isfabricated into duct frames with suitable connecting means, with theframes serving as joints and supports for the paneling. The paneling isintermittantly joined and supported over the periphery of the moldingframe with the inner periphery of the frame consisting of the end flangeof the molding sequentially bent to bring the ends of the moldingtogether in an enclosed perimeter. The other end flange, intermediateflange and web are severed to free the flange for bending. The panelingjoint is achieved by frictional engagement between the beads on theflanges of the molding and the paneling. The friction force occurs whenthe paneling is deformed upon insertion in the molding, with theresiliency or rebound characteristics of the paneling giving rise to anormal force against the beads which constrict the paneling fromreturning to the shape prior to deformation, that is, the pre-stressedshape of the paneling.

Further, the molding frame is uniquely amenable to longitudinal supportsfor the duct, thereby providing for rigid duct suspension as well asduct support in all directions.

The molding provides a simply fabricated, light weight, ductile joint toreplace the taped and stapled joint for duct board. A seal of a dualnature by virtue of a bead contacting both faces of the panelinginserted in the molding is a feature in addition to the mechanicalgripping of the beads. Further enhancing of the seal between mold andpaneling is achieved by the flow path pattern which any leakage isforced to follow because the path is made more intricate by the uniquemating of the molding to the paneling.

Other objectives of the molding are the lower cost of the aluminumextrusion over the prior art steel supports, and further economicsavings in the case of assembly in place over the taped joint.

The duct system of molding frame and duct board or the like typepaneling provides a rigid structure to replace the weaker duct systemwhere duct segments were butted and taped together. The addition oflongitudinal support in conjunction with the molding frame results in arigid support structure for panel type ducts which rigidity was onlyachieved by sheet metal ducts in the prior art.

Further objects of the present invention are a duct system which can berigidly suspended, exceptionally well adapted to systems with largerpressure differentials from one side of the duct surface to the other,and more economical due to greater ease in field installation.

BRIEF DESCRIPTION OF THE DRAWINGS The above objects and advantages ofthe invention will become readily apparent to one skilled in the artfrom reading the following detailed description of an embodiment of theinvention when considered in the light of the accompanying drawings, inwhich:

FIG. I is a fragmentary perspective view of a moldmg;

FIG. 2 is a typical assembly of duct board and longitudinal supportbetween two pieces of molding;

FIG. 3 is a fragmentary perspective view of a longitudinal support;

FIG. 4} is an end view of a duct for a positive pressure system;

FIG. 5 is an enlarged fragmentary view of the connecting means for themolding in FIG. 4 with portions of the duct wall broken away to revealthe connection;

FIG. 6 is an end view of a duct for a negative pressure system; and

FIG. 7 is an enlarged fragmentary view of the mold connecting means inFIG. 6.

DESCRIPTION OF THE PREFERRED EIVBODIMENT Referring to the drawings, FIG.1 illustrates an aluminum extrusion molding ill with a rectangular web12 from which end flanges l4 and 16 extend symmetrically and at rightangles to the web 12, being affixed to the edges of the web 12 oversubstantially the entire length of the web 12. One end flange 16 isshorter in width than the other end flange 14. The shorter end flange 16has the corners extending over the length of the end flange l6 andfacing the other end flange 14 rounded with a radius 18. From the faceof the other end flange 14, which face is oriented toward the shorterflange 16, extend beads 20. The beads 20 cover the length of the endflange 14 extending at right angles to and located at the outerextremities of the end flange 14. A rectangular intermediate flange 22extends from and is affixed to the web 12 being located in between andoriented parallel to the end flanges. This intermediate flange 22 is ofa width identical to the longer end flange M with beads 2% along thelength thereof duplicating and located opposing the beads 20 on thelonger flange. While this molding is an extrusion of non-corrosivealuminum, clearly the molding could be made of other materials and byprocesses other than extruding.

Two features of the molding are its ability to mechanically gripinsulating board of a thickness equal to or exceeding the distancebetween opposed faces of end flange l4 and intermediate flange 22 aswell as structural members having a press fit with the opposed faces ofend flange 16 and intermediate flange 22, and the sealingcharacteristics of the beads 28 located on the flanges 14 and 22.

The mechanical gripping by the molding 10 is twofold. First, the beads20 on the mating flanges 14 and 22 constrict insulating board of aresilient nature when such board is forced into the molding l0, andsecond, the shorter end flange 16, in conjunction with the intermediateflange 22, provides a force fit joint for additional support members.The frictional force from both joints is sufficient to result in rigidstructures.

The seal between the molding l0 and insulating board resulting from thebeads 20 constricting the insulating board is enhanced by the resiliencyof the board against the beads 2t! and further creates a maze type pathfor the flow pattern of any leakage.

These molding 10 features will be better understood when applied to theduct system described below, but it should be understood that themolding 10 of the present invention is not limited to use for ductsystems only.

The unique combination of molding 10, insulating board and longitudinalsupport is illustrated in the typical assembly of FIG. 2. Two moldings10 are illustrated in end view between which a duct board 24 is supported by mating flanges 14 and 22 with beads 20 actually deforming theduct board 24. The distal spacing of the opposing beads 20 being lessthan that between the flanges 14 and 22, enhances the gripping andsealing between duct board 24 and molding 10. Due to the resilientnature of the duct board 24, the deformation is not of a permanentnature with the duct board returning to the shape prior to insertioninto the molding it] upon removal. This elasticity ability or resilientnature maintains, in effect, a pressure seal between duct board 24 andbeads 20 while the deformation of the duct board 24 enhances thegripping of the duct board 24 by the molding 10, since in addition tothe frictional holding force arising from the rebound of the duct boardagainst the beads 20, the duct board 24 is mechanically worked inpassing over the beads 20 upon being pulled from the mold. Clearly,where a low density board or possibly one without elasticity is used theratio of open distance between flanges l4 and 22 to the open distancebetween opposing beads 20, resulting from the closing off of the openingbetween flanges l4 and 22 by the beads 20, can be varied to accommodateeven those materials which simply displace the volume bounded by beads20, flanges l4 and 22, and web 12.

Where required in extreme cases, such as high pressure duct systems, anadhesive can be applied between the duct board 24 and the web 12 tofurther enhance sealing and gripping.

The duct board 24 is typically a fibrous glass compressed mat which isresin bounded and cured to give it elasticity, with a scrim reinforcedfoil liner affixed to one face with flame retardant adhesive.

For additional support and rigidity, the ends of a longitudinal support26 can be press fitted between the short end flange 16 and intermediateflange 22 of the molding 10, as illustrated in FIG. 2. The grippingfeature of the molding 10 described above can now be seen to provide notonly support means for the longitudinal support 26, but a structural tiebetween the molding 10. The structural tie will be seen to form a boxconstruction in conjunction with the molding 10 when the duct systemconstruction is explained below. In addition, the longitudinal support26, being centered on the face of the duct board 24, provides rigidsupport at the point of maximum moment and deflection of the duct board24. This type deflection of the duct board 24 has been a detriment toduct systems of wide span having large face surface areas, especiallywhen used in combination with substantial pressure differential from oneside of the duct board 24 to the other. Such deflection or bowing tendsto pull the mating joints where the duct board 24 is butted together,apart, thereby weakening the joint and giving rise to possible leakageproblems.

The longitudinal support 26, illustrated in FIG. 3, is typically analuminum extrusion, but in similarity to the molding could be fabricatedor otherwise constructed as well as being made of other materials. Thechannel type cross-section of the longitudinal support 26 results instructural rigidity. The flanges 28 in conjunction with the channel legsto which the flanges 28 are affixed form resilient members which canreadily be forced between the shorter end flange 16, plus the leadingsurface provided by the intermediate flange 22 extending beyond the endflange 16, further aiding insertion. Once inserted, the longitudinalsupport flanges 28 and the back 29 of the channel shape create a forcewhich is normal against the shorter end flange 16 and the intermediateflange 22, respectively. This orienta tion of the longitudinal supportplaces the back 29 of the channel shape against the duct board 24providing a wide face area for supporting the duct board 24.

FIG 4 illustrates the further utility of the molding in a positivepressure duct system. The typical system illustrated consists of asingle piece of molding ll} bent into a rectangular frame with the innerflange of the frame being the larger end flange 14. The remainingflanges 16 and 22 and the web 12 are cut normal to the face of the bentflange 14 at the point of bending to free the larger end flange 14 forbending. Three 90 bends are imparted to the larger end flange 14resulting in the two ends of the molding being brought together. Theseends are then fastened by a flat angle 38 which is screwed to themolding web 12 with metal screws 40. The. frame now being formed, theduct system is completed by inserting duct board 243 of the glassfibrous nature and in the manner described above and illustrated in FIG.2. For a rectangular duct, as illustrated in FIG. 4, the duct board 24consists of four rectangular pieces of board which overlap at thecorners. These corners are then taped along the length of the duct toform a gas tight periphery for the duct. The tape 34 is typically anacqueous thermo-setting flame retardant type, but can be of othersuitable types such as pressure sensitive tape. Further, the presentinvention is not limited to the use of glass fibrous duct board 24 asdescribed in the typical embodiment, but rather any board withsufficient volume displacement or elasticity to exert force against thebeads 2%) of the molding it} is suitable. Repetition of the fabricationsteps described above with molding it periodically interspaced betweensuitable lengths of duct board 24 results in the capability to constructa duct of any desired length.

The type of frame formed from the molding l0, illustrated in FIG. 4, inthe typical embodiment of the invention is most suitable for ducts withsmall perimeteis which can be fabricated from a single piece ofreasonable length molding. As duct size increases, the availability ofthe required length of molding it} may well dictate that the frame bemade of two bent pieces of molding 11') or possibly four pieces ofmolding l0.

Where the length or width spans of the duct board of the duct in thetypical embodiment of FIG. 4 are long enough to require support againstbowing, the longitudinal support 26 illustrated can be added. Thelongitudinal support 26 is inserted into the molding and held asdescribed and illustrated above in FIG. 2 by a friction force arisingfrom the force tit between the longitudinal support 26 and the molding10. The longitudinal support 26 is located in the middle of the ductboard 24 where the maximum deflection of the duct board 24 would occur.Since the duct system illustrated in FIG. 4 is a positive pressuresystem with the internal duct pressures exceeding those outside theduct, the longitudinal support 26 is placed with the back 29 facing theoutside of the duct board 24 resulting in any deflection tendency in theduct board 24 being prevented when the duct board 24 is pushed outwardagainst the longitudinal support 26. Clearly, the application of thelongitudinal support 26 is available over I the periphery of the ductand in the typical embodiment of the invention, in FIG. 4, where theduct is rectangular, the longitudinal support is applicable to all foursides.

Further, where four supports are used, it is obvious that a box has beenformed to encase the duct in all directions while at the same timeproviding a longitudinal support structure for the duct which isstructurally independent of the duct board 24. Since the friction forcewhich retains the longitudinal support 26 in the molding 10 also resistsremoval of the longitudinal support 26 from the molding 10, a duct frameof a very rigid nature results. When this type structure is suspendedfrom a ceiling by angles 36 or the like type structural supportsfastened to the molding 10 by metal screws 32, a rigid suspension systemresults. A system with this type of rigidity is not possible where theduct board 24 is relied on as a structural member due to the boards moreflexible nature.

It becomes apparent that two distinct duct systems are available throughuse of the molding 10 of the present invention, those using molding l0and duct board 24, only, for less demanding pressure systems of asmaller size, and those of a larger size with pressure which tends tobow the duct board 24 and which therefore require in addition,longitudinal supports 26.

The molding m and longitudinal support 26 can be reversed, whenfabricated, to place the shorter end flange 16 of the molding it) on theinside of the duct. This places the longitudinal support, when used,within the duct also. This type construction is suitable for negativetype pressure systems where the pressure outside the duct exceeds thatwithin the duct. Such a system is illustrated in FIG. 6. Insertion andoverlapping of the duct board duplicates that of the positive pressuresystem as does that of sealing the corner joints with tape 34 andsuspending the duct system by use of angles 36 attached to the molding10 with metal screws 32. But the molding 10 is bent on the shorter endflange 16 with the longer end flange 14, intermediate flange 22 and web12 being severed at the joints to be bent to free the shorter end flange16 for bending. Reversal of the longitudinal support results in the back29 of the channel like structure again facing the duct board 24, but nowbeing in a position to resist deflection of the duct board 24 inward dueto the external pressure on the duct board 24 being greater than thepressure within the duct system. While only one longitudinal support 2sis shown, as in the positive pressure system, longitudinal supports 26are applicable over the entire periphery of the duct.

HG. 7 illustrates the connecting means for the molding iii in HQ. 6consisting of a flat angle 38 attached to the web l2 between the shorterend flange 16 and the intermediate flange 22 with metal screws 40. Theconnection completes the periphery of the frame encompassed by themolding it) making the periphery continuous.

it becomes apparent that the present invention may be used in modifiedforms other than those of the typical embodiment. For example, clearlyonly two flanges l4 and 22 having beads 20 and a web 12 are necessary tomake the molding l adaptable to receive panelling, and it is furthersufficient if the flanges 14 and 22 extend from the web 12 in onedirection only to form a shape similar to a structural channel. Theflanges l4 and 22 need not be parallel.

Where sealing is not a prime consideration, the beads 26 may beintermittant rather than continuous over the length of the flanges 14and 22. The beads 20 need not be located at the longitudinal edge of theflanges 1d and 22 but simply spaced out away from the web 12.

When the web 12 is extended beyond either flange 14 and 22, employed inthe channel shape described above, the web 12, becomes a tab which isuseful as an attaching means where the panelling in the form of a ductis to be butted against a wall and the molding used as a terminatingmeans.

Again, while the above channel shape is combined in a back to backarrangement for butt connecting panelling in the typical embodiment, theorientation could just as easily be that of having one channel shape atright angles to the other, with the legs of the channel, flanges 14 and22, extending outwardly, to form a corner molding M).

The present invention is a molding 10 which, when combined wifli alongitudinal support 26 and duct board 24, forms a duct system.

The molding, being an aluminum extrusion, is lighter in weight than thesteel supports of the prior art and also non-corrosive. The greaterductility of the aluminum molding over steel makes the aluminum moldingsuitable for forming by bending and fabricating with the use of metalscrews. The beads 20 on the molding lb provide not only a structuralgripping support but a seal as well. This seal is further enhanced bythe shape of the molding 110 which, in conjunction with the duct board24 creates an intricate path for any potential leakage to follow with abead seal inside as well as outside.

The greater flexibility of the molding 10 makes it especially suitablefor duct systems formed basically of duct board 24 wherein the moldingit) in the form of a frame provides both a suspension means andconvenient joint for butting the duct boards as well as periphialsupport. The butted joint between duct boards is such that the joiner oftwo segments of a duct system can be accomplished in place, next to aceiling, for instance, with lateral movement which is more easilyaccomplished than taping the joint as in the prior art.

With the addition of a longitudinal support 26 or supports rigiditypreviously unavailable, outside of in metal duct systems, is obtainablemaking rigid installations possible as well.

The aluminum molding E0 is more economical than steel molding and alsoless expensive from the standpoint of fabrication in duct systems beingeasy to form into frames, having simple force fits for duct board 24 andlongitudinal supports 26, and eliminating the taped joint which is oftendifficult to achieve with the duct in place.

In accordance with the provisions of the patent statutes, we haveexplained the principle and mode of operation of our invention and haveillustrated and described what we now consider to represent its bestembodiment. However, we desire to have it understood that the inventionmay be practiced otherwise than as specifically illustrated anddescribed without departing from its spirit or scope.

What is claimed is:

l. A duct comprising:

a frame transverse with respect to said duct and generally defining thecross-sectional configuration of said duct, said frame comprising amolding having first and second flanges spaced with respect to eachother and joined by a web, said molding being closed upon itself withthe web lying in a plane transverse with respect to said duct, saidfirst and second flanges having opposed major faces, said first flangehaving a bead extending longitudinally thereof and projecting toward theopposed major face of said second flange, said second flange having abead extending longitudinally thereof and projecting toward the opposedmajor face of said first flange, said beads being spaced from said weband each other, panelling of yieldable resilient material, saidpanelling having transverse edges which are greater in thickness thanthe spacing between said beads and substantially equal to the spacingbetween said flanges, said transverse edges of said panelling beingfitted between said beads of said molding whereby said beads compressand frictionally engage said panelling to impede any flow of fluidsbetween said panelling and said molding, said panelling having at leasttwo longitudinal edges extending from said transverse edges and inproximity to each other, and means to couple said proximate longitudinaledges to form a duct.

2. The duct according to claim 1 wherein said panelling has a thicknessless than the spacing of said flanges and greater than the spacingnormal of said flanges between said beads.

3. The duct according to claim 1 wherein said web extends beyond saidfirst flange on the side of said flange opposite said second flange andincluding a third flange atfixed to said web and generally parallel tosaid first flange a given distance therefrom, and a structural memberhaving a portion of a thickness to fit between said third and firstflanges with a press fit has an edge received between said third andfirst flanges whereby said molding and said structural member aresecured together.

4. The duct according to claim 3 wherein there are a pair of said frameswhich are spaced from each other and said structural member is alongitudinal support extending between said frames and having an edgeportion press fitted between said third and first flanges of each frame.

5. The duct according to claim 4 wherein said structural member is ofelongated form having a major element having a front and rear face andat least one flange extending from said front face of said major elementa distance from said rear face of said major element correspondinggenerally to a distance greater than the spacing between said third andfirst flanges whereby said element and flange have a press fit betweensaid third and first flanges.

6. The duct according to claim 5 wherein said rear face of said majorelement is adjacent said panelling.

7. The duct according to claim 6 wherein said panelling is closed uponitself in planes perpendicular to the plane of said web to form a closedduct adapted a convey fluids under positive pressure relative toambient, and wherein said third flange of said molding is exterior ofsaid closed duct.

8. The duct according to claim 6 wherein said panelling is closed uponitself in planes perpendicular to the plane of said web to form a closedduct adapted to convey fluids under negative pressure relative toambient, and wherein said third flange of said molding is within saidclosed duct.

9. The duct according to claim 1 including fourth and fifth flanges onsaid molding complementary to said first and second flanges respectivelyand extending from an opposite side of said web in registry with saidfirst and second flanges, said fourth and fifth flanges having opposedmajor faces, a bead extending longitudinally of said fourth flange andprojecting toward the opposed major face of said fifth flange, a beadextending longitudinally of said fifth flange and projecting toward theopposed major face of said fourth flange, each of said beads on saidfourth and fifth flanges being spaced from said web, additionalpanelling of yieldable resilient material, said additional panellinghaving transverse edges which are greater in thickness than the spacingbetween said beads of said fourth and fifth flanges and substantiallyequal to the spacing between said fourth and fifth flanges, saidtransverse edges of said additional panelling being fitted between saidbeads on said fourth and fifth flanges, said additional panelling havingat least two longitudinal edges extending from said transverse edgesthereof and in proximity to each other, and means to couple saidproximate longitudinal edges of said additional panelling to form a ductsection.

10. The duct according to claim 1 wherein said panelling is a mat ofresin bounded glass fibers.

1. A duct comprising: a frame transverse with respect to said duct andgenerally defining the cross-sectional configuration of said duct, saidframe comprising a molding having first and second flanges spaced withrespect to each other and joined by a web, said molding being closedupon itself with the web lying in a plane transverse with respect tosaid duct, said first and second flanges having opposed major faces,said first flange having a bead extending longitudinally thereof andprojecting toward the opposed major face of said second flange, saidsecond flange having a bead extending longitudinally thereof andprojecting toward the opposed major face of said first flange, saidbeads being spaced from said web and each other, panelling of yieldableresilient material, said panelling having transverse edges which aregreater in thickness than the spacing between said beads andsubstantially equal to the spacing between said flanges, said transverseedges of said panelling being fitted between said beads of said moldingwhereby said beads compress and frictionally engage said panelling toimpede any flow of fluids between said panelling and said molding, saidpanelling having at least two longitudinal edges extending from saidtransverse edges and in proximity to each other, and means to couplesaid proximate longitudinal edges to form a duct.
 2. The duct accordingto claim 1 wherein said panelling has a thickness less than the spacingof said flanges and greater than the spacing normal of said flangesbetween said beads.
 3. The duct according to claim 1 wherein said webextends beyond said first flange on the side of said flange oppositesaid second flange and including a third flange affixed to said web andgenerally parallel to said first flange a given distance therefrom, anda structural member having a portion of a thickness to fit between saidthird and first flanges with a press fit has an edge received betweensaid third and first flanges whereby said molding and said structuralmember are secured together.
 4. The duct according to claim 3 whereinthere are a pair of said frames which are spaced from each other andsaid structural member is a longitudinal support extending between saidframes and having an edge portion press fitted between said third andfirst flanges of each frame.
 5. The duct according to claim 4 whereinsaid structural member is of elongated form having a major elementhaving a front and rear face and at least one flange extending from saidfront face of said major element a distance from said rear face of saidmajor element corresponding generally to a distance greater than thespacing between said third and first flanges whereby said element andflange have a press fit between said third and first flanges.
 6. Theduct according to claim 5 wherein said rear face of said major elementis adjacent said panelling.
 7. The duct according to claim 6 whereinsaid panelling is closed upon itself in planes perpendicular to theplane of said web to form a closed duct adapted a convey fluids underpositive pressure relative to ambient, and wherein said third flange ofsaid molding is exterior of said closed duct.
 8. The duct according toclaim 6 wherein said panelling is closed upon itself in planesperpendicular to the plane of said web to form a closed duct adapted toconvey fluids under negative pressure relative to ambient, and whereinsaid third flange of said molding is within said closed duct.
 9. Theduct according to claim 1 including fourth and fifth flanges on saidmolding complementary to said first and second flanges respectively andextending from an opposite side of said web in registry with said firstand second flanges, said fourth and fifth flanges having opposed majorfaces, a bead extending longitudinally of said fourth flange andprojecting toward the opposed major face of said fifth flange, a beadextending longitudinally of said fifth flange and projecting toward theopposed major face of said fourth flange, each of said beads on saidfourth and fifth flanges being spaced from said web, additionalpanelling of yieldable resilient material, said additional panellinghaving transverse edges which are greater in thickness than the spacingbetween said beads of said fourth and fifth flanges and substantiallyequal to the spacing between said fourth and fifth flanges, saidtransverse edges of said additional panelling being fitted between saidbeads on said fourth and fifth flanges, said additional panelling havingat least two longitudinal edges extending from said transverse edgesthereof and in proximity to each other, and means to couple saidproximate longitudinal edges of said additional panelling to form a ductsection.
 10. The duct according to claim 1 wherein said panelling is amat of resin bounded glass fibers.